1. Field of the Invention
The present invention relates to a computer system, a PC card, and a connecting structure between the PC card and the computer system. More particularly, the invention relates to a technique that is effectively applied to a connecting structure between the PC card for wireless LAN and an antenna in the computer system.
2. Background
Recently, as the use of the Internet or corporate intranet spreads, a means for connection with a communication network such as a telephone network or LAN (local area network) is becoming essential to PC (personal computer) users. Specifically, attention is focused on the wireless communication technology using wireless LAN, which can make the best possible use of the portability characteristic of notebook PCs. Against the background of this, notebook PCs capable of wireless communication which have antennas previously mounted in their housings are now being received in the market.
The notebook PC capable of wireless communication is designed, for instance, so that a slit antenna (aperture antenna) is previously provided in its housing, for instance, in the rear side of a liquid crystal display panel, enabling a wireless LAN card (wireless module) to be added as an option when desired by the user. The optional wireless LAN card provides a design that can reduce the initial price and flexibly to meet the user""s needs.
A wireless LAN card compliant with, for instance, the mini PCI (peripheral component interconnect) bus standard can be employed. The mini PCI bus standard adds an expansion card to the PCI bus, and it enables about a 60% reduction in size compared with the conventional PCI card thereby contributing to miniturization and cost-reduction. Alternatively, a card compliant with the PCMCIA (personal computer memory card international association) standard may be used.
However, there is the following problem for the wireless module to be built in the mini PCI standard card slot. That is, to efficiently transmit a weak radio frequency signal such as that of a mobile phone or wireless LAN, the antenna and the wireless module are connected by a cable, and it is required to establish impedance matching between the antenna and the cable and between the cable and the wireless module. For the wireless LAN, a coaxial cable is essential as the cable because the frequency used is in a 2.5 GHz band. FIG. 6 illustrates the problem of connecting the wireless module and the antenna. FIG. 6(a) is a plan view showing part of a wireless module and a motherboard, and FIG. 6(b) shows a cross section of a notebook PC. Coaxial cable 101 LED from antenna 100 is connected to the upper surface side of motherboard 102 by coaxial connector 103. Coaxial connector 103 is connected to coaxial connector 104 through a conductor passing through motherboard 102, and connected to coaxial cable 105. The other end of coaxial cable 105 is connected to coaxial connector 107 on card board 106 of the wireless module, and connected to radio frequency module 109 through wiring 108. With such connection, a complete shield is provided between the output end of the wireless module and the antenna, and in addition, impedance matching can be provided using standard cables and connectors.
However, the spatial limit allowed by the mini PCI standard is 2.4 mm for the component height and 5 mm for the whole card thickness. It is required to use a coaxial connector fulfilling such spatial limit to connect the wireless module and the coaxial cable. In FIG. 6, such a condition is required at least for coaxial connector 107.
In the state of the art, two types of connectors are known as coaxial connectors satisfying the above spatial condition. One is a coaxial connector made by a cutting process, and the other one is a coaxial connector made by a pressing process. The connector made by a cutting process is characterized by easy attachment and detachment, though it is expensive. The connector made by a pressing process is characterized by requiring a large mating and unmating force and hence a special tool for attachment or detachment, though it is inexpensive.
When applying these connectors in products, low cost is a large motivation for adoption. Accordingly, it is desirable to employ the product by pressing. However, when the cable management as shown in FIG. 6 is employed, a special tool is required for installing the wireless module. For the service of installing the wireless module when it is shipped from the factory, it is necessary to distribute the special tool to perform the installation work. There is a problem that a customer not having the special tool cannot perform the installation by themself in the setup at the customer""s site after buying a computer.
Although it is possible to directly connect the cable to card board 106, bypassing motherboard 102, as shown in FIG. 7, it may be obvious that it does not lead to a solution of the above described problem.
On the other hand, it is possible to transmit a radio frequency signal through line-type connector 110 to be connected to the edge terminal of card board 106, without employing the cable management as in FIG. 6. However, no consideration is usually given to impedance matching in the connection between the card terminal and line-type connector 110, and thus there is a problem that the signal attenuation (insertion loss) in the connector portion is significant.
It is an object of the present invention to provide a radio frequency transmission technique which realizes, in the standard for expansion cards such as the existing mini PCI, impedance matching performance equivalent to the connection made by a coaxial connector at low cost and with high workability.
The invention of this application is briefly described as follows. That is, the computer system of the present invention consists of a first board, a first signal line formed on the first board, a plurality of first ground lines formed adjacent the first signal line, in spaced and parallel relation to each other, a second board, a second signal line formed on the second board, a plurality of second ground lines formed adjacent the second signal line, in spaced and parallel relation to each other, and a connecting structure for connecting the first board and the second board, the connecting structure electrically connecting the first ground lines and the second ground lines, and electrically connecting said first signal line and the second signal line.
The above connecting structure has a first construction in which the connecting structure is a connector, which is disposed on the first board and has an opening into which part of the second board is inserted, or a second construction in which the connecting structure includes a first connector disposed on the first board, and a second connector disposed on the second board and inserted into the first connector, or a third construction in which the connecting structure is ball bumps or pin terminals arranged in a grid on the second board.
Further, the computer system of the present invention can have the first signal line and the second signal line in multiple numbers, and the first signal lines and the first ground lines may be alternately disposed, and the second signal lines and the second ground lines may be alternately disposed.
Further, the computer system of the present invention has a radio frequency module on the second board, and the second signal line is connected to the radio frequency terminal of the radio frequency module, the multiple number of second ground lines are connected to the ground terminals of the radio frequency module, and a radio frequency signal is transmitted through the first signal line, connecting structure, and second signal line.
Further, the computer system of the present invention has a coaxial receptacle on the first board, and the central conductor of the coaxial receptacle is connected to the first signal line, the outer conductors of the coaxial receptacle are connected to the multiple number of first ground lines, and into the coaxial receptacle is a coaxial plug at an end of a coaxial cable, the other end of which is connected to an antenna structure.
Further, the coaxial receptacle and the coaxial plug are made by a pressing process, and the height of the first board in the direction of the normal thereto can be made about 2.4 mm or lower when they are connected together.
In accordance with the computer system of the present invention, the computer system does not have a coaxial connector on the second board provided with a radio frequency module, and a radio frequency signal is transmitted through the connecting structure by which the second board is connected to the first board. This allows the installation of the second board to be easily made when shipped from the factory, or at the customer""s site. On the other hand, the transmission of the radio frequency signal through the connecting structure is carried out by the signal lines on the first and second boards and a multiple number of ground lines which are disposed in parallel adjacent the signal lines. In accordance with the examination by the present inventors, even if the connecting structure and the signal lines, which are the input and output of the connecting structure, are not completely shielded, impedance matching can be provided to the extent that there is no problem in practical use, by employing a coplanar structure sandwiching the signal lines with the ground lines.